Organic Light Emitting Display (OLEO) display device with self-luminous, low driving voltage, high luminous efficiency, short response time, high resolution and contrast, nearly 180° viewing angle, wide using temperature range, to achieve flexible display and large area panchromatic display and many other advantages, is recognized as the industry's most promising display device.
OLEDs can be classified into passive matrix OLEDs, PMOLEDs and active matrix OLEDs, AMOLEDs according to driving modes, namely, direct addressing and thin film transistor matrix addressing two categories. Wherein, AMOLED has a matrix arrangement of pixels, belonging to the active display type, high luminous efficiency, usually used for high resolution large-size display device.
AMOLED is a current-driven device. When a current flows through the organic light emitting diode, the organic light emitting diode emits light, and the emitting luminance is determined by the current flowing through the organic light emitting diode itself. Most existing integrated circuits (ICs) only transmit voltage signals, so AMOLEDs pixel driving circuit needs to complete the task of converting voltage signals into current signals. Conventional AMOLED pixel driver circuit is usually 2T1C, that is, two thin-film transistors and a capacitor structure, the voltage is converted to current. As the threshold voltage to drive the thin film transistor shifts, the current flowing through the organic light emitting diode changes greatly, resulting in the unstable emitting of the organic light emitting diode, and the luminance is very uneven, greatly affecting the display effect of the image. To solve the above problem, a compensation circuit needs to be added to each pixel. The compensation means that the threshold voltage to drive the thin film transistor in each pixel must be compensated, so that the current flowing through the organic light emitting diode becomes independent of the threshold voltage.
As shown in FIG. 1, a 7T2C AMOLED pixel driving circuit includes seven thin film transistors and two capacitors, and are respectively a first thin film transistor T10, a second thin film transistor T20, a third thin film transistor T30, a fourth thin film transistor T40, a fifth thin film transistor T50, a sixth thin film transistor T60, a seventh thin film transistor T70, a first capacitor C10, and a second capacitor C20. The pixel driving circuit needs to be controlled by four scan control signals, respectively are a first scan control signal S10, a second scan control signal S20, a third scan control signal S30, and a fourth scan control signal S40. An operation timing diagram of the circuit is as shown in FIG. 2, the operation process of the circuit includes: a first phase 10, a second phase 20, and a third phase 30, wherein in the second phase 20, a low potential is provided after a high potential, the second scan control signal S20 first provides a high voltage and then a low voltage. When the second scan control signal S20 provides a low voltage, by the function of the first capacitor C1, causing the potential of the connection point of the first capacitor C1 and the second capacitor C2 is unstable, and the pixel driving circuit needs seven thin film transistors and two capacitors, the structure is complex, the effective light emitting area of the pixel is low, and the number of scan control signals is large, so that the timing controller is also relatively complex.